Accumulated Other Comprehensive Income (Loss) (Components of OCI) (Details 1) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Before Tax		$ 399,354	$ 133,553	$ (174,347)
Other Comprehensive Income (Loss), Income Tax		(99,335)	(34,087)	37,510
Other Comprehensive Income (Loss), Net of Tax		300,019	99,466	(136,837)
Foreign Currency Translation Adjustment [Member]
Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax			5,371
Other Comprehensive Income (Loss) before Reclassifications, Tax			0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		31,642	5,371
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax			2,011
Reclassification from AOCI, Current Period, Tax			0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		0	2,011
Other Comprehensive Income (Loss), Before Tax		31,642	7,382	(35,584)
Other Comprehensive Income (Loss), Income Tax		0	0	0
Other Comprehensive Income (Loss), Net of Tax		31,642	7,382	(35,584)
Pension and Other Postretirement Plans [Member]
Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		266,520	164,527
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		3,899	(97,864)	(42,563)
Reclassification from AOCI, Current Period, Tax		(1,053)	26,422	11,492
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		2,846	(71,442)	(31,071)
Other Comprehensive Income (Loss), Before Tax		368,994	127,515	(139,314)
Other Comprehensive Income (Loss), Income Tax		(99,628)	(34,430)	37,614
Other Comprehensive Income (Loss), Net of Tax		269,366	93,085	(101,700)
Net Actuarial Loss [Member]
Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax		365,164	231,104	(101,013)
Other Comprehensive Income (Loss) before Reclassifications, Tax		(98,594)	(62,398)	27,273
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		266,570	168,706	(73,740)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	1,219	(2,046)	(11,349)
Reclassification from AOCI, Current Period, Tax		(329)	552	3,064
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		890	(1,494)	(8,285)
Net Prior Service Cost [Member]
Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax		(69)	(5,725)	4,262
Other Comprehensive Income (Loss) before Reclassifications, Tax		19	1,546	(1,151)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(50)	(4,179)	3,111
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	2,680	(4,142)	(947)
Reclassification from AOCI, Current Period, Tax		(724)	1,118	256
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1,956	(3,024)	(691)
Curtailments and settlements Included in Net Income [Member]
Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	0	(91,676)	(30,267)
Reclassification from AOCI, Current Period, Tax			24,752	8,172
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(66,924)	(22,095)
Cash Flow Hedges
Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(1,476)	(906)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		487	(95)
Other Comprehensive Income (Loss), Before Tax		(1,282)	(1,344)
Other Comprehensive Income (Loss), Income Tax		293	343
Other Comprehensive Income (Loss), Net of Tax		$ (989)	$ (1,001)
Cash Flow Hedges
Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Before Tax				551
Other Comprehensive Income (Loss), Income Tax				(104)
Other Comprehensive Income (Loss), Net of Tax				$ 447

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension and postretirement plan cost (see Note 15) and are included in non-operating pension and postretirement benefit income in the Company’s Consolidated Statements of Operations.